3D Tibial Acceleration and Consideration of 3D Angular Motion Using IMUs on Peak Tibial Acceleration and Impulse in Running

Abstract

Purpose: Peak tibial acceleration (PTA) is defined as the peak acceleration occurring shortly after initial contact, often used as an indirect measure of tibial load. As the tibia is a rotating segment around the ankle, angular velocity and angular acceleration should be included in PTA. This study aimed to quantify three-dimensional tibial acceleration components over two different sensor locations and three running speeds, to get a better understanding of the influence of centripetal and tangential accelerations on PTA typically measured in running. Furthermore, it explores tibial impulse as an alternative surrogate measure for tibial load.

Methods: Fifteen participants ran 90 s on a treadmill at 2.8, 3.3, and 3.9 m·s -1 , with inertial measurement units (IMUs) located distally and proximally on the tibia.

Results: Without the inclusion of rotational accelerations and gravity, no significant difference was found between axial PTA between both IMU locations, whereas in the tangential sagittal plane axis, there was a significant difference. Inclusion of rotational accelerations and gravity resulted in similar PTA estimates at the ankle for both IMU locations and caused a significant difference between PTA based on the distal IMU and PTA at the ankle. The impulse showed more consistent results between the proximal and distal IMU locations compared with axial PTA.

Conclusions: Rotational acceleration of the tibia during stance differently impacted PTA measured proximally and distally at the tibia, indicating that rotational acceleration and gravity should be included in PTA estimates. Furthermore, peak acceleration values (such as PTA) are not always reliable when using IMUs because of inconsistent PTA proximally compared with distally on an individual level. Instead, impulse seems to be a more consistent surrogate measure for the tibial load.

FIGURE 1

Distal (above ankle) and proximal (below knee) IMU on the tibia of the dominant leg. Left: frontal plane view, IMUs shown as originally attached to the tibia in Ψ_IMUp and Ψ_IMUd. Right: sagittal plane view, IMU CS shown as rotated based on principal component analysis (see “Data Processing”) into Ψ_IMUpfand Ψ_IMUdf.

FIGURE 2

All tibial acceleration components from equations 2 and 4 visualized in the complete stance phase for one participant at 3.3 m·s⁻¹ at the proximal IMU location. Axes shown in the Ψ_IMUf CS. Mean over 30 strides visualized with a shaded SD. Impulse window also visible.

FIGURE 3

Difference of PTA_anklez versus PT_AIMUz based on the proximal and distal IMU locations.

FIGURE 4

PTA estimates versus the impulse, as a mean of over 30 strides of each participant. Data shown for 2.8, 3.3, and 3.9 m·s⁻¹ including Pearson correlation (r) for each speed.